This invention relates to rotary sprinkler heads and, more particularly, to sprinkler heads that nutate (i.e., wobble while they rotate) to minimize the “donut effect” prevalent with conventional rotary sprinkler heads.
Conventional rotary sprinklers typically throw one or more streams in a radial direction to wet a specified area in a circular pattern. In circumstances where the sprinkler is in a fixed location, unless some mechanism is employed to break up the one or more streams, a donut pattern is created that leaves a substantial dry area inside the pattern. A higher speed of rotation tends to break down the stream or streams, but also shortens the throw radius. An alternative is the wobbling-type sprinkler where a water-deflection plate is caused to wobble as it rotates (sometimes referred to as a nutating action). Various nutating or wobbling sprinkler head designs have been available but with potential shortcomings that can nullify the very effect that makes such sprinklers attractive in the first instance. Examples of known nutating or wobbling sprinkler heads may be found in U.S. Pat. Nos. 5,381,960; 5,950,927; and 6,932,279. Commonly owned U.S. Pat. Nos. 5,439,174; 5,588,595; 5,671,885; 6,267,299; and 6,439,477 provide further examples.
A problem often encountered with sprinklers of this type relates to stalling, primarily at start-up, but possibly also during normal operation. Stalling occurs when the water-deflection plate of the sprinkler head fails to tilt at start-up, or ceases tilting during operation, thereby simply rotating (without wobbling) and distributing a stream particularly susceptible to the donut effect. When nutating or wobbling sprinklers operate as designed, the wobbling action tends to fill in the pattern in a substantially uniform manner. Thus, it is critical that the water-deflection plate reliably and consistently remain in a tilted orientation on start-up and while rotating to achieve the desired wobbling action.